Having problems fixing this nasty and annoying interference/ground loop or ground problem. It can not be re-created it is totally random. The only thing I've noticed is that it tends to only happen if volume has been above 25-30 but not every time. I've checked all my head unit connections...
Before assuming he should set LPF at 80 lets find out the frequency range the driver supports first and go from there. Especially since he is complaining from top end output and you're telling him to cut it off with a filter...